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 Hu Chunming
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/*!
@file
Defines `boost::hana::reverse`.
Copyright Louis Dionne 2013-2022
Distributed under the Boost Software License, Version 1.0.
(See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
*/
#ifndef BOOST_HANA_REVERSE_HPP
#define BOOST_HANA_REVERSE_HPP
#include <boost/hana/fwd/reverse.hpp>
#include <boost/hana/at.hpp>
#include <boost/hana/concept/sequence.hpp>
#include <boost/hana/config.hpp>
#include <boost/hana/core/dispatch.hpp>
#include <boost/hana/core/make.hpp>
#include <boost/hana/length.hpp>
#include <cstddef>
#include <utility>
namespace boost { namespace hana {
//! @cond
template <typename Xs>
constexpr auto reverse_t::operator()(Xs&& xs) const {
using S = typename hana::tag_of<Xs>::type;
using Reverse = BOOST_HANA_DISPATCH_IF(reverse_impl<S>,
hana::Sequence<S>::value
);
#ifndef BOOST_HANA_CONFIG_DISABLE_CONCEPT_CHECKS
static_assert(hana::Sequence<S>::value,
"hana::reverse(xs) requires 'xs' to be a Sequence");
#endif
return Reverse::apply(static_cast<Xs&&>(xs));
}
//! @endcond
template <typename S, bool condition>
struct reverse_impl<S, when<condition>> : default_ {
template <typename Xs, std::size_t ...i>
static constexpr auto reverse_helper(Xs&& xs, std::index_sequence<i...>) {
return hana::make<S>(
hana::at_c<sizeof...(i) - i - 1>(static_cast<Xs&&>(xs))...
);
}
template <typename Xs>
static constexpr auto apply(Xs&& xs) {
constexpr std::size_t N = decltype(hana::length(xs))::value;
return reverse_helper(static_cast<Xs&&>(xs), std::make_index_sequence<N>{});
}
};
}} // end namespace boost::hana
#endif // !BOOST_HANA_REVERSE_HPP
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